Lockstitch sewing machines and related rotary hooks or CB-hooks are well known and therefore will not be described herein, where we simply remember schematically the composition of the hooks in which the lockstitch is formed between the bobbin thread (wound around the bobbin contained in the hook) and the needle thread, which at each stitch, must wrap the bobbin with its loop.
The rotary hook, in execution with bobbin case, comprises at least one hook body, which is connected to a shaft from which it receives motion and comprises a circular cavity of the hook body, a basket free to rotate inside the circular cavity of the hook body and which in turn comprises a well of the basket, a gib which helps to constrain the basket to the hook body and a bobbin case, which is housed in the well of the basket and which helps to constrain the bobbin to the basket.
The shaft can be integral with the body hook or housed in a hole present at the center of the circular cavity of the hook body.
The bobbin case containing the bobbin with the bobbin thread, is assembled and disassembled by the operator of the sewing machine at each change of the bobbin, through an axial translation, in which the outer diameter of the bobbin case is inserted inside the inner diameter of the well on the basket and the shaft of the well of the basket, if present, is inserted into the central hole of the shaft of the bobbin case (in fact there are some embodiments of the rotary hooks in which bobbin case and basket do not have the central shaft in order to allow the use of coreless bobbins), while an angular reference ensures its correct angular positioning with respect to the basket.
Very similar is the assembly and disassembly operation of the bobbin case in CB-hooks. However, the difference is that, since there is no basket, the bobbin case is bound directly to the shaft of the hook body formed in the circular cavity of the CB-hook body itself, instead on the basket as occurs in rotary hooks. For CB-hooks, this is the only way to constrain the bobbin case to the hook body, since the bobbin case must be free to rotate around said shaft of the hook body.
The axial constraint of the bobbin case on the basket (or respectively on the CB-hook body), to prevent accidental disassembly during the sewing operation, occurs by means of the slide of the bobbin case that engages itself on the basket (or respectively on the CB-hook body). The leverage created by the lever on the slide allows to retract and release the slide from the basket (or respectively from the CB-hook body) through the actuation of the lever, and then to release the bobbin case from the axial constraint to allow disassembly through an axial translation.
That axial restraint is provided by the interlock of the slide, in its position at rest, i.e. forward, in an undercut formed in the basket (or respectively in the CB-hook body): in rotary hooks in execution of the basket with shaft and in CB-hooks, this undercut is constituted by a groove on the shaft of the basket (or respectively on the shaft of the CB-hook body), which engages the edge of the central hole of the slide, while in the rotary hooks in execution of the basket without shaft (possible indeed only in rotary hooks), such undercut is constituted by a groove in the internal diameter of the well of the basket that engages the front end of the slide, in correspondence to the claw formed at one end of the slide (described later and in the following called slide's claw for simplicity), which, in the slide's position at rest, i.e. forward, protrudes from the outer diameter of the bobbin case. This protrusion from the bobbin case of the front end of the slide is also present on the bobbin case for CB-hooks, but in this case it cannot be used to constrain axially the bobbin case to the CB-hook because, in CB-hooks, the bobbin case, as said, must be free to rotate around the shaft of the hook body.
The slide in turn is constraint to the bobbin case by a guide that allows only its translational movement forward (position at rest in which the slide and the bobbin case are constrained to the basket or, respectively, to the hook body in the CB-hooks) and backward (disengagement position of the slide, in which it is possible the assembly and disassembly of the bobbin case from the basket or, respectively, from the hook body in the CB-hooks), where said backward position is reached consequently to the activation of the lever. The lever, by means of an interlock or of a pin that secures it to the slide, creates with said slide a leverage, which has the fulcrum on the bobbin case body. The whole set of slide and lever is also referred to as the latch. During the assembly, the lever is positioned in the working position, after the insertion of the slide into the guide on the bobbin case body, and while it creates the leverage, it also determines the backward and forward working stroke's end points of the slide. Note that in order to assemble the slide on the bobbin case through the insertion of the slide into the guide on the bobbin case, it is necessary to provide a through opening on the wall of the bobbin case for the passage of the slide's claw Said opening has the disadvantage to interrupt the continuity of the profile of the bobbin case to support the passage of the needle thread. Said slide's claw has the function to constrain temporarily the bobbin to the bobbin case, when the slide is retracted for the assembly and disassembly of the bobbin case on the basket (or respectively on the CB-hook body) in order to avoid that the bobbin falls out from the bobbin case during these operations. On the contrary, when the bobbin case is assembled and constrained on the basket (or respectively on the CB-hook body), and the slide is then in its forward position at rest, also the slide's claw is forward and leaves free to rotate within the bobbin case, for the sewing operation, the bobbin, which is now constrained axially by the basket (or respectively by the CB-hook body). When the slide is forward and at rest (as occurs during the sewing operation), the slide's claw protrudes from the outer diameter of the bobbin case and, in most cases of the rotary hooks, it—the slide's claw—is housed within a space formed in the wall of the basket, so to not hamper the passage of the needle thread, which during the sewing wraps the bobbin case and is supported in its passage by the basket. More critical instead is the passage of the needle thread over the bobbin case on CB-hooks and in some executions of the bobbin case on rotary hooks, on which the side wall of the basket in correspondence to the slide's claw is not present, as, not being there present the basket to offer support to the needle thread, said needle thread leans directly on the bobbin case and both said protrusion of the slide from the bobbin case and the interruption of the continuity of the profile of the bobbin case in correspondence to the through opening on the wall of the bobbin case, required to pass the slide's claw during the assembly operation of the slide, can represent an hindrance.
In order to avoid the slide's claw to protrude from the outer wall of the bobbin case at rest and to facilitate the passage of the needle thread loop during the sewing, in the bobbin cases for CB-hooks and in some executions of the bobbin case for rotary hooks, in which the wall of the basket in correspondence to the slide's claw is not present (as for example for the bobbin cases for the so-called WHEELER & WILSON rotary hook family or for the oversized bobbin cases designed to contain larger bobbins), the thickness of the wall of the bobbin case in correspondence to the slide's claw has been increased so to contain it entirely within said thickness: or the outer diameter of the bobbin case is eccentric with respect to the inner one, or the plan profile of the outer wall of the bobbin case is shaped, or a protuberance, even only partial, is present on the outer diameter of the bobbin case in correspondence to the slide's claw.
To allow the assembly of the slide on the bobbin case, however, the through opening on the wall of the bobbin case is always present. Said through opening represents always a hindrance to the passage of the needle thread loop during the sewing operation, as it offers an interrupted profile (and not continuous as is in the case of the wall of the basket), from which said needle thread is supported.
A possible solution to avoid the through-opening and therefore to continue to have a continuous profile even in absence of the basket's wall, is illustrated by the EP0457376B1 patent where it shows a different assembling system of the slide by means of partialization of one edge of the guide of the slide on the bobbin case and rotation of the slide on the other edge for the insertion of the slide into the guide during the assembly.
In the state of the art (and also in EP0457376B1 patent) the slide is constituted by one single component commonly obtained by shearing and bending of a metal sheet (followed by eventual operations of chips removal as milling) with a thickness generally of at least 1 mm, in order to give sufficient strength to the slide. The bending is necessary to obtain the slide's claw, which, seen from the side, comes to assume a shape of a “C”. The internal profile of the “C” and its position with the slide at rest, are determined by the functional requirements related to the traverse travel stroke of the slide and the diameter of the bobbins to be constrained. Once so defined the internal profile of the slide's claw, the overall dimensions of such slide's claw towards the outside of the bobbin case, is consequence of the bending of the sheet and the thickness of the sheet itself. The thickness of the sheet is in turn determined by the functional requirements of the guide of the slide on the bobbin case and the leverage created with the lever and is usually of at least 1 mm, while for the sole slide's claw function also a much less thickness would be enough.
WO-A-2014/035132 describes a sewing machine hook that envisages various conformations of slides made always and only of one single piece. Also in FIGS. 5 and 6, the additional protuberance 550, is formed in one only piece with the slide 520.
Object of the present invention is to implement a hook comprising a bobbin case with an improved slide, composed of multiple components, in order to achieve new performances than those attainable at the state of the art in which the slide is made of one single mechanical part.